ES6--symbol

1.symbol实例分析

'use strict'
let getName =Symbol('name');//Symbole定义的不是一个字符串
module.exports=class User{

    [getName](){
        return 'ggb'
    }

    print(){
        console.log(this[getName]())
    }

}

下面写一个代码引用上面代码

const User =require('./005.symbole.js')
let getName =Symbol('name');
var user =new User();
user.print();//ggb
user[getName]();//error    1111

可以看到 1111处代码报错了，此处可以作为私有成员访问的一个很好的例子。

2.使用一般的遍历不能得到symbol类型的值

'use strict'
let name =Symbol('name');
var obj={
    age:22,
    [name]:"ggb"
}

var keys=Object.keys(obj);
console.log(keys)//['age']
let key
for(key in obj){
    console.log(key)  //age
}
let key2=Object.getOwnPropertySymbols(obj)[0]
console.log(obj[key2]);// 'ggb'

3.symbol取值

'use strict'
var name1=Symbol.for('name')
var name2=Symbol.for('name')
console.log(name1===name2);//true
console.log(Symbol.keyFor(name1));//'name'

4. of用法

let arr=[1,2,3];
for( let item of arr){
    console.log(item) //分行打印出1，2,3
}

5.symbole与iterator结合

let arr=[1,2,3];

var iterater =arr[Symbol.iterator]();  
console.log(Symbol.iterator)//Symbol(Symbol.iterator)
console.log(typeof arr[Symbol.iterator])//function
console.log( arr[Symbol.iterator])//[Function: values]
console.log(iterater.next());//{ value: 1, done: false }
console.log(iterater.next());//{ value: 2, done: false }
console.log(iterater.next());//{ value: 3, done: false }
console.log(iterater.next());//{ value: undefined, done: true }
let getName =Symbol('name');
console.log(typeof getName) //symbol
console.log(getName)//Symbol(name)

6.symbole与for of 结合

/**
 * Created by Administrator on 2017/6/11.
 */
'use strict'
class UserGroup{

    constructor(users){
        this.users=users;
    }

    [Symbol.iterator](){
        let i=0;
        const names=Object.keys(this.users)
        let length=names.length;
        let self=this;
        return {

            next:function(){
                let name=names[i++];
                let qq=self.users[name];
                return {value:{name,qq},done:i>length}
            }

        }
    }
}

let group =new UserGroup({name:'ggb',age:'28'})
for(let u of group){
    console.log(u);
}
let iterator =group[Symbol.iterator]();
console.log(iterator.next());
console.log(iterator.next());
console.log(iterator.next());

打印结果为：

{ name: 'name', qq: 'ggb' }
{ name: 'age', qq: '28' }
{ value: { name: 'name', qq: 'ggb' }, done: false }
{ value: { name: 'age', qq: '28' }, done: false }
{ value: { name: undefined, qq: undefined }, done: true }

7.改良版

let obj={name:'ggb',age:'28'};
let iteratorFunc=function(){
        let i=0;
        const names=Object.keys(this)
        let length=names.length;
        let self=this;
        return {

            next:function(){
                let name=names[i++];
                let qq=self[name];
                return {value:{name,qq},done:i>length}
            }

        }
}
obj[Symbol.iterator]=iteratorFunc;
for(let item of obj){
    console.log(item);
}

打印结果

{ name: 'name', qq: 'ggb' }
{ name: 'age', qq: '28' }

8.iterator

var obj={
    length:2,
    '0':"aaa",
    '1':"bbb",
}
obj[Symbol.iterator]=[][Symbol.iterator];
for(let i of obj){
    console.log(i);
}
'ggb'[Symbol.iterator];
for(let i of 'ggb'){
    console.log(i);
}